Nightmare

Mana cost: {5}{B}
Type: Creature — Nightmare Horse
Power / toughness: * / *
Set: The List #W17-17 (rare)
Price: $0.40 USD

Flying (This creature can't be blocked except by creatures with flying or reach.)
Nightmare's power and toughness are each equal to the number of Swamps you control.

Nightmare has 28 printings, first in Unlimited Edition (1993). EDHREC ranks it #14,304 among Commander cards. It appears most in Korlash, Heir to Blackblade decks (826 on EDHREC). It has 4 official rulings.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: legal
pioneer: legal
standard: not legal
brawl: legal

Commanders that run Nightmare most

Deck counts from EDHREC.

Often played with Nightmare

Cards that show up in the same decks on EDHREC.

Rulings

2008-04-01: If you control 0 swamps, then the Nightmare has 0 toughness and will be put into its owner’s graveyard as a state-based action right before the next player gains priority.
2009-10-01: Nightmare’s power and toughness changes as the number of Swamps you control changes.
2013-07-01: Nightmare’s ability counts all lands you control with the subtype Swamp, not just ones named Swamp.
2013-07-01: The ability that defines Nightmare’s power and toughness works everywhere, not just on the battlefield.

Nightmare

Legality

Commanders that run Nightmare most

Often played with Nightmare

Rulings

Printings